Coronadoa demisispira n. sp.

Figure 9

Type material. Holotype (LACM 3113: Fig. 9 C). Paratypes: 26–40 m, Farnsworth Bank, off S side of Catalina Island, California, USA, 33.350˚N, 118.517˚W (LACM 3114); 13–30 m, Cortez Bank, 0.5 mile south of Bishop Rock, California, USA, 32.433˚N, 119.125˚W (LACM 3115: Fig. 9 A–B). All LACM type material leg. J. McLean.

Type locality. 26–40 m, Farnsworth Bank, off S side of Catalina Island, California, USA, 33.350˚N, 118.517˚W.

Additional material examined. 10–23 m, NW side of Guadalupe Island, (Pilot Rock and 5 miles S), Baja California, Mexico, 29.188˚N, 118.253˚W (LACM 72-121, 1). 20–26 m, SW side Natividad Island, Baja California, Mexico, 27.888˚N, 115.212˚W (LACM 72-117, 1). 13–17 m, 5 fathom Bank about 4 miles SW of SE tip of Cedros Island, outer coast Baja California, Mexico, 27.983˚N, 115.212˚W (LACM 71-93, 2). 26 m, San Miguel Island, California, USA, 34.020˚N, 120.402˚W (DLG 1131, 1). 46 m, off Santa Cruz Island, California, USA, 34.056˚N, 119.961˚W (DLG 1263, 3).

Etymology. demisi-: Latin for sunken; -spira: Latin for spire. Referring to the flat spire of the species.

Description. Shell small (to 0.75 mm), trochiform depressed. Protoconch of 0.875 whorls, embryonic cap without sculpture, remainder with strong axial ribs, no apertural varix, apertural margin prosocline. Teleoconch of 1.5 whorls, 11–13 raised axial cords, indistinct at suture and towards umbilicus, most pronounced at periphery, interstices with irregular axial growth marks; no spiral sculpture. Umbilicus open, occasionally undersurface of protoconch visible, bordered by knobby carina towards base. Aperture subquadratic D-shaped, lower adumbilical corner pronounced, forming knobby carina of umbilicus. Operculum thin, round, multispiral, nucleus central.

Differential diagnosis. The sympatric C. simonsae Bartsch, 1946 (Fig. 9 A–B and Fig. 10 A,C; Fig. 9 C and Fig. 10 B) is proportionally taller (width to height: simonsae mean = 1.28, SD = 0.047, n = 4; demisispira mean = 1.79, SD = 0.22, n = 4; t-test t = -4.36, p = 0.022). As a corollary, its umbilicus is wider, and tends to have fewer axial cords per unit whorl. The degree of axial sculpturing is variable in both species, from distinct cords to raised lamellae. Coronadoa hasegawai Geiger & Sasaki, 2009, from temperate Japan is as tall as C. simonsae .

Remarks. Coronadoa demisispira is much less common than C. simonsae; if the two species are present in the same lot, C. demisispira comprises at most 10% of C. simonsae specimens. This skewed ratio suggests that the two are not dimorphic males and females of the same species. In general, Vetigastropoda show a male:female ratio of close to 1:1 (Bretos et al. 1985, Hooker & Creese 1995, Wells & Malay 1995), although there are no data on Scissurellidae s.l.